Accompanying the widespread conversion of many types of content, such as movies, music, books, etc., to digital formats has been the development of a number of systems for protecting such content against unauthorized access, reproduction, and distribution. In many such protection systems, the content is encrypted such that access requires a decryption key, which is made available under terms agreeable to the content owner/provider.
To prevent unauthorized reproduction and redistribution of such protected content, the encryption key is often also made dependent on some unique or relatively unique identifier associated with the original storage medium or device to which the content is bound. This dependency can be implemented using, for example, a cryptographic function of the identifier. If the content is copied to another storage medium or device, the decryption key formed using the identifier of that other medium or device will be different from the original encryption key, thereby preventing access to the unauthorized copy.